Blank samples comprise reference material with a grade less than the detection limit or should be close to zero, blanks are usually composed of material such as quartz, limestone, granites or basalt or any materials which ensured have grades lower than detection limit. Blanks are very useful in testing samples laboratory preparation and controlling contamination effect, usually it's inserted into sample batch after mineralised samples or main mineralised zones. There are most common two scenarios: * if it was inserted after the meniralised zones and its results recording assays, it should be reviewed the laboratory preparation and the cleanliness. * When it was inserted into expected low grade samples and its results recording high assays, it has been swapped during samples preparation and we can ensure that from our geological logging. It's common that blanks have some assays but it must be very close to the detection limits or until (10) times of it will be acceptable.